The six suspects arrested in a federal sting in Hampden on Thursday planned to kill a co-conspirator in a robbery who was actually an undercover ATF agent, according to court documents.

Unbeknownst to the suspects, the robbery plot was a ruse — part of a series of Baltimore operations set up by the Bureau of Alcohol, Tobacco, Firearms and Explosives in recent months. For the second time, gunfire erupted in a public place as authorities moved in for the arrest, this time in the 3300 block of Clipper Mill Rd.

According to a complaint filed Friday in federal court, Blake and Tracey Betters and Brandon Harris are “armed drug traffickers active in the Waverly neighborhood” who control a stretch of Greenmount Avenue and are suspects in several commercial and residential armed robberies.

ATF officials, who have declined to discuss the operations in detail, said Thursday that the suspects were “very violent individuals, who intended to do some serious harm.”

“The police did their job,” Marino Vidoli, the acting special agent in charge of the ATF’s Baltimore field office, said at the scene Thursday.

On May 9, a source working with the ATF met with Tracey Betters and asked him and two associates if they were interested in participating in a robbery of a drug stash house where kilograms of cocaine were being stored. A second meeting took place May 29, with Tracey Betters saying “he and his crew were ready to complete the robbery,” according to court documents.

Later that day, the source introduced them to an undercover ATF agent, who said the robbery would net 10 kilograms of cocaine that could be re-sold for $400,000. The suspects asked questions and discussed how the operation would unfold, records show.

“We know what we’re doing,” Harris said, according to a taped conversation described in court documents. “We’re not kids.”

The ATF source picked up Tracey Betters Thursday morning in eastern Baltimore, where a red truck circled his vehicle, records show. When the car left, he told the source, “You’re clean.” At another location, McLaurin climbed in with two bulletproof vests; Betters had a shotgun and a pistol.

On the way to Clipper Mill Road, according to the complaint, Tracey Betters proposed that the suspects and confidential source kill the undercover officer once the robbery was complete and take his share of the stolen cocaine.

As they discussed the robbery, they also agreed that they would have to kill a man who they were told would be guarding the stash house, according to the affidavit.

Officials said the suspects’ car rammed into police vehicles before they were taken into custody. Stun grenades, which witnesses said produced the sound of explosions, were used to disorient the suspects.

“What this shows is that day in and day out, our officers are putting their lives on the line to get these criminals off the street,” said ATF spokesman Michael Campbell.

The court documents do not say which one of the suspects was shot, but Blake Betters was the only one who did not make an initial appearance in U.S. District Court on Friday.

Benjamin entered the courtroom missing a shoe, which he apparently lost while trying to flee. “I’m not gonna lie, I was scared,” Benjamin told U.S. Magistrate Judge Stephanie Gallagher before being instructed not to speak by his attorney.

Though the stash house was fictional, the men’s recorded statements of an intent to steal large amounts of drugs allow prosecutors to charge them with conspiracy to possess with intent to distribute a controlled substance, as well as conspiracy to possess a firearm in furtherance of a drug-trafficking crime.

They each face a maximum sentence of life in prison, with a mandatory minimum of 10 years in prison, if convicted of the drug charges.

Such ruses have been used at least twice in recent months by the ATF, and they mirror operations by other federal agencies to catch suspected terrorists. In one Maryland case, a Woodlawn man had discussions with undercover agents about blowing up a Catonsville Army recruiting center and drove their with what he thought was a bomb supplied by authorities. The suspect, Antonio Martinez, was sentenced to 25 years in federal prison in April.

Blake and Tracey Betters, of the 5100 block of Benton Heights Ave. in Northeast Baltimore, were both indicted in Baltimore Circuit Court on drug charges on June 7, records show.

McLaurin and Harris were charged together in 2008 with attempted first degree murder, though all charges were dropped by city prosecutors a year later, court records show. McLaurin was also charged in 2006 with rape, and was convicted of second-degree assault.